Die stacking apparatus and method

ABSTRACT

Various stacked semiconductor devices and methods of making the same are provided. In one aspect, a method of manufacturing is provided that includes providing a first semiconductor die that has a first bulk semiconductor side and a first opposite side. A second semiconductor die is provided that has a second bulk semiconductor side and a second opposite side. The second opposite side of the second semiconductor die is coupled to the first opposite side of the first semiconductor die. Electrical connections are formed between the first semiconductor die and the second semiconductor die.

This application is a divisional of prior application Ser. No.11/832,519, filed Aug. 1, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to semiconductor processing, and moreparticularly to semiconductor device mounting apparatus and methods.

2. Description of the Related Art

Conventional integrated circuits are frequently implemented on asemiconductor substrate or die that consists of a small rectangularpiece of semiconductor material, typically silicon, fashioned with twoopposing principal sides. The active circuitry for the die isconcentrated near one of the two principal sides. The side housing theactive circuitry is usually termed the “active circuitry side,” whilethe side opposite the active circuitry side is often termed the “bulksilicon side.” Depending on the thermal output of the die, it may bedesirable to mount a heat transfer device, such as a heat sink, on thebulk silicon side of the die. This mounting may be directly on the bulksilicon side or on a lid that is positioned over the die.

A conventional die is usually mounted on some form of substrate, such asa package substrate or a printed circuit board. Electrical connectivitybetween the die and the underlying substrate or board is establishedthrough a variety of conventional mechanisms. In a so-called flip-chipconfiguration, the active circuitry side of the die is provided with aplurality of conductor balls or bumps that are designed to establish ametallurgical bond with a corresponding plurality of conductor padspositioned on the substrate or circuit board. The die is flipped overand seated with the active circuitry side facing downwards on theunderlying substrate. A subsequent thermal process is performed toestablish the requisite metallurgical bond between the bumps and thepads. One of the principal advantages of a flip-chip mounting strategyis the relatively short electrical pathways between the integratedcircuit and the substrate. These relatively low inductance pathwaysyield a high speed performance for the electronic device.

In some circumstances it may make sense from a performance standpoint tostack one semiconductor die on another semiconductor die. For example,it may be advantageous to mount a memory device on a processor device.However, electrical interconnects must be established between thestacked dice. Several conventional techniques for stacking dice havebeen considered.

In one conventional variant, a relatively small semiconductor die ispositioned on the bulk semiconductor side of a much larger semiconductordie. Bonding wires are used to establish the electrical conductivitybetween the upper die and the lower die. The difficulty associated withthis approach is that the bonding wires tend to be relatively longelectrical pathways and thus exhibit higher than desired inductance andproportionally slower electrical performance. In addition, the bulksemiconductor side is not available for heat sink mounting.

In another conventional variant, a relatively small die is flip-chipmounted on the bulk silicon side of a larger semiconductor die.Electrical interconnects between the upper and lower die are provided bya plurality of conductor traces that are formed on the bulk silicon sideof the lower die. As with the first-mentioned conventional design, theconductor traces represent relatively high inductance pathways and thuslimit speed performance. Furthermore, the bulk silicon side is notavailable for a heat sink

In still another conventional design, a second die is mounted on thebulk silicon side of a larger die. Electrical interconnects between thetwo are established through a plurality of silicon vias. This designalso requires a plurality of external traces and thus represents longerthan desired electrical pathways for signal transfer. In addition, thebulk silicon side is not available for a heat sink

A fourth conventional design consists of a first die upon which a coupleof additional dice are positioned. The multiple smaller dice areelectrically interconnected with each other and with the larger base dieby way of a metal layer that is patterned on the base die and the twotop-mounted dice. The metal layer is not unlike a larger scale versionof a typical metallization layer used in a semiconductor die. In thisregard, a dielectric layer is typically formed over the base die and themultiple top-mounted dice. The dielectric layer is lithographicallypatterned with openings to selected portions of the base and top-mounteddice. The metallization layer is thereafter deposited over thedielectric layer. This conventional technique requires a very highdegree of die alignment, which is not always possible and thus mayresult in limited yields.

The present invention is directed to overcoming or reducing the effectsof one or more of the foregoing disadvantages.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method ofmanufacturing is provided that includes providing a first semiconductordie that has a first bulk semiconductor side and a first opposite side.A second semiconductor die is provided that has a second bulksemiconductor side and a second opposite side. The second opposite sideof the second semiconductor die is coupled to the first opposite side ofthe first semiconductor die. Electrical connections are formed betweenthe first semiconductor die and the second semiconductor die.

In accordance with another aspect of the present invention, a method ofmanufacturing is provided that includes providing a first semiconductordie that has a first bulk semiconductor side and a first opposite side.A plurality of second semiconductor dice is provided, each of whichincludes a second bulk semiconductor side and a second opposite side.The second opposite sides of the plurality of second semiconductor diceare coupled to the first opposite side of the first semiconductor die.Electrical connections between the first semiconductor die and theplurality of second semiconductor dice are formed.

In accordance with another aspect of the present invention, an apparatusis provided that includes a first semiconductor die that has a firstbulk semiconductor side and a first opposite side. A secondsemiconductor die has a second bulk semiconductor side and a secondopposite side. The second opposite side of the second semiconductor dieis coupled to the first opposite side of the first semiconductor die.The second semiconductor die includes electrical connections with thefirst semiconductor die.

In accordance with another aspect of the present invention, an apparatusis provided that includes a first semiconductor die that has a firstbulk semiconductor side and a first opposite side. A plurality of secondsemiconductor dice is included. Each of the second semiconductor diceincludes electrical connections with the first semiconductor die and hasa second bulk semiconductor side, and a second opposite side that iscoupled to the first opposite side of the first semiconductor die.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the invention will become apparentupon reading the following detailed description and upon reference tothe drawings in which:

FIG. 1 is a pictorial view of an exemplary embodiment of a semiconductordevice that includes stacked semiconductor dice;

FIG. 2 is a sectional view of FIG. 1 taken at section 2-2;

FIG. 3 is a sectional view of an exemplary embodiment of semiconductordie illustrating an exemplary conductor layer fabrication;

FIG. 4 is a sectional view like FIG. 3 depicting an exemplary process offabricating conductor structures on the semiconductor die;

FIG. 5 is a sectional view like FIG. 4 depicting an exemplary process ofstacking two exemplary semiconductor dice;

FIG. 6 is a sectional view like FIG. 5 depicting an exemplary process ofencapsulating portions of the semiconductor device;

FIG. 7 is a sectional view like FIG. 6, but depicts additionalprocessing of the exemplary semiconductor device;

FIG. 8 is an exploded pictorial view of an exemplary embodiment of asemiconductor device depicting some exemplary mounting configurations;

FIG. 9 is a plan view of an alternate exemplary embodiment of asemiconductor device including multiple semiconductor dice stacked onanother semiconductor die; and

FIG. 10 is a sectional view of another alternate exemplary embodiment ofa semiconductor device including stacked semiconductor dice.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

In the drawings described below, reference numerals are generallyrepeated where identical elements appear in more than one figure.Turning now to the drawings, and in particular to FIG. 1, therein isshown a pictorial view of an exemplary embodiment of a semiconductordevice 10 that includes a semiconductor die 20 and a semiconductor die30 mounted on the semiconductor die 20. An insulation or encapsulationlayer 40 is positioned on the semiconductor die 20. A portion of theinsulation layer 40 is shown cut away to reveal a portion of thesemiconductor die 30. The conductor structures 45 are designed toprovide interconnects between the semiconductor device 10 and anotherdevice as described elsewhere herein. The semiconductor dice 20 and 30may be any of a myriad of different types of circuit devices used inelectronics, such as, for example, microprocessors, graphics processors,application specific integrated circuits, memory devices or the like,and may be single or multi-core. The semiconductor dice 20 and 30 may befabricated using silicon, germanium or other semiconductor materials. Ifdesired, the semiconductor dice 20 and 30 may be fabricated assemiconductor-on-insulator substrates. Several conductor structures 45are coupled to the semiconductor die 20. The conductor structures 45 maybe fabricated as solder structures of lead-based or lead-free soldersand shaped as bumps, balls or other structures. In an exemplaryembodiment, a silver-tin-copper solder may be used. Optionally, anothertype of conductor structure may be used.

Additional details of the semiconductor device 10 may be understood byreferring now also to FIG. 2, which is a sectional view of FIG. 1 takenat section 2-2. The semiconductor die 20 includes a bulk semiconductorside 50 and an opposite side 55. Chip circuitry of the semiconductor die20, represented schematically by the dashed box 60 may be fabricatednear the side 55. The semiconductor die 30 includes a bulk semiconductorside 65 and an opposite side 70. Chip circuitry of the semiconductor die30, represented schematically by the dashed box 75, may be fabricatednear the side 70. Thus, the opposite side 70 of the semiconductor die 30is coupled to the opposite side 55 of the semiconductor die 20. Thisarrangement provides certain advantages described in more detail below.

Exemplary electrical connections between the semiconductor die 20 andthe semiconductor die 30 will now be described. The semiconductor die 20may be provided with plural conductor structures 80 proximate the side55. The conductor structures 80 may be bond pads or other types ofconductor structures composed of, for example, copper, nickel, gold,platinum, silver, alloys of these or the like. In an exemplaryembodiment, the conductor structures 80 are composed of an alloy ofcopper, nickel and gold. The semiconductor die 30 may be provided withplural conductor structures 90 proximate the side 70. The conductorstructures 90 may be bond pads or other types of conductor structures,and composed of the same types of materials used for the conductorstructures 80. Ohmic contact between the pluralities of conductorstructures 80 and 90 may be provided by another plurality of conductors100 interposed between the sets of conductor structures 80 and 90. Theconductors 100 may be composed of solder or other conductor materials.If solder is used, the conductor structures 100 may be fabricated asbumps, balls or other structures and be lead-based or lead-free. In anexemplary embodiment, a silver-tin-copper solder may be used.

This illustrative embodiment provides very short electrical pathways andthus fast signal and power transfer between the semiconductor die 20 andthe semiconductor die 30. In addition, the bulk semiconductor side 50 isunfettered, leaving open the possibility of mounting a heat sink (notshown) thereon.

The semiconductor die 20 may be electrically connected to the conductorstructures 45 by plural conductor structures 110 positioned proximatethe side 55, a metal layer 120 positioned on or proximate the side 55and plural conductors 130 coupled between the conductor structures 45and the metallization layer 120. Optionally, a pathway between a givenconductor 110 and a given conductor 45 may be provided with a conductor120, but without the metallization layer 125. Such an arrangement isshown for the conductor 110, the conductor 125 and the conductor 45located at the position labeled A in FIG. 2. Thus, the conductors 130may have corresponding conductors 45 and vice versa. The conductorstructures 110 may be bond pads or other types of conductor structurescomposed of the same types of materials used for the conductorstructures 110. The metal layer 120 may be a so-called redistributionlayer that provides electrical pathways between the various conductorstructures 110 of the semiconductor die 20 and the conductor structures45. When viewed from above, the metallization layer 120 may take on theform of electrical traces that are well known for use on printed circuitboards and other types of electrical substrates. The benefits of routingmay be achieved with two or more of the conductors 130 and theconductors 110 connected to the layer 120, however, the number andarrangement of conductor structures 110 and 130 tied to the layer 120are matters of design discretion. The metal layer 120 may be composed ofa myriad of conductor materials, such as copper, nickel, gold, platinum,silver, alloys of these or the like. The conductors 130 may be posts,pillars or other type of mechanical structures and may be composed of,for example, copper, nickel, gold, platinum, silver, alloys of these orthe like. In an exemplary embodiment, the conductor structures 130 arecomposed of an alloy of copper, nickel and gold. The conductors 130should project farther away from the side 55 of the semiconductor die 20than does the side 65 so that clearance for the semiconductor die 30 isprovided.

The encapsulation layer 40 surrounds the metallization layer 120 and theconductor structures 130 and thus provides lateral support for theconductor structures 130. In addition, the encapsulation layer serves asan underfill material for the region between the semiconductor device 30and the semiconductor device 20. The encapsulation layer 40 may befabricated from well-known encapsulation materials, such as epoxy resinwith or without fillers such as silica or the like. If desired, theencapsulation layer 40 may be fabricated as a laminate structure.Optionally, a separate underfill material (not shown) of epoxy resin orother well known under fill materials, may be positioned between thesemiconductor dice 20 and 30.

An exemplary process for fabricating the semiconductor device 10 may beunderstood by referring now to FIGS. 3-7 and initially to FIG. 3. Themetallization layer 120 is formed on the surface 55 of the semiconductordevice 20. A variety of techniques may be used, such as plating,chemical vapor deposition, physical vapor deposition or the like. It ispreferable that the metallization layer 120 includes an opening 140 toaccommodate the positioning of the semiconductor device 30 shown inFIGS. 1 and 2. Thus, the metallization layer 120 will establish ohmiccontact with the conductor structures 110 but not with the conductorstructures 80 that are destined for electrical connectivity with thesemiconductor device 30 depicted in FIGS. 1 and 2. If desired, themetallization layer 120 may be built up as a laminate structure.

The formation of the conductor structures 130 is depicted in FIG. 4. Inan exemplary embodiment, a mask of resist or other mask material 160 isformed on the semiconductor die 20 and patterned with openings, one ofwhich is shown and labeled 165, in which a metallic material may bedeposited to establish the conductor structures 130. As noted above, theconductor structures 130 may be composed of, for example, copper,nickel, gold, platinum, silver, alloys of these or the like. Followingthe formation process for the structures 130, the resist film 160 may beremoved by well-known ashing or other resist stripping techniques.

Referring now to FIG. 5, the semiconductor device 30 may be flip-chipmounted on the semiconductor die 20 in the opening 140 of themetallization layer 120 by way of the conductor balls or bumps 100. Asnoted above, electrical pathways are established between thesemiconductor die 30 and the semiconductor die 20 by way of theconductor structures 90 on the device 30, the bumps 100 and theconductor structures 80 on the semiconductor die 20. The conductorstructures 100 may be coupled first to the semiconductor device 30 or tothe device 20 as desired. Following the initial mounting, a reflowprocess may be performed to temporarily liquify the conductor structures120. In an exemplary embodiment, the semiconductor device 10 may beheated from about 35° C. up to about 240° C. in about 20 to 120 secondsand then allowed to cool. Optionally, the conductor structures 100 maybe formed by reflowing complementary solder structures on both the pads80 and 90. As noted above, the conductor structures 130 should projectfarther away from the side 55 of the semiconductor die 20 than does thesemiconductor die 30.

The formation of the encapsulation layer 40 will now be described inconjunction with FIGS. 6 & 7. The encapsulation layer 40 may be appliedto the semiconductor device 10 to encapsulate not only the semiconductordevice 30 but also the underlying conductor structures 130 and themetallization layer 100. If desired, the semiconductor die 30 may beless than completely encapsulated. The encapsulation layer 40 may becomposed of well-known epoxy materials, such as epoxy resin with orwithout silica fillers and phenol resins or the like. Optionally, thelayer 40 may be formed from a synthetic rubber mixture of epoxy resin,phenol resin, fused silica, and synthetic rubber. It is anticipated thatthe encapsulation layer 40 may be initially deposited with a greaterheight than that of the conductor structures 130 as shown.

In order to establish ohmic contact between the subsequently positionedconductor structures 45 (See FIGS. 1 & 2) and the conductor structures130, it may be necessary to perform a material removal process, such asa grinding or chemical mechanical planarization process on theencapsulation layer 40. FIG. 7 depicts the semiconductor device 10following the material removal process. The tops 170 of the conductorsstructures 130 are exposed and ready for attachment of the conductors 45depicted in FIGS. 1 and 2. The conductor structures 45 may be formed bya variety of processes. If solder balls are used, a drop-in process maybe used. Bumps may be formed by well-known plating or stencil processes.If other than solder structures are used, then other well-knowntechniques may be used.

With the semiconductor device 30 mounted on the side 55 of thesemiconductor device 20, the bulk semiconductor side 50 of thesemiconductor die 20 is still available for positioning of a heat sinkAs shown in FIG. 8, which is an exploded pictorial, the semiconductordevice 10 may be positioned on another device 180 such that the bulksemiconductor side 50 of the semiconductor die 20 may receive a heatsink 185. The device 180 may be a substrate, a printed circuit board, orother type of substrate. The heat sink 185 may be a fin, pipe or otherconfiguration and may include fluid cooling. Additionally, the device180 may, in turn, be mounted to another electronic device, such asanother printed circuit board, or other type of substrate as desired.For example, the device 180 may be a package substrate and the device190 may be a printed circuit board. The devices 180 and 190 may be partof some overall system, such as a computer system, or a component of acomputer system, such as a discrete board or card.

In the embodiment disclosed in FIGS. 1 and 2, a single semiconductor die30 is mounted on the semiconductor die 20. However, it should beunderstood that multiple semiconductor devices may be mounted on anothersemiconductor device in the same fashion as the semiconductor die 30 ismounted on the semiconductor die 20 depicted in FIGS. 1 and 2. In thisregard, FIG. 9 depicts an overhead view of a semiconductor die or device195 upon which three semiconductor dice or devices 200, 210 and 215 aremounted. The devices 195, 200, 210 and 215 may be any of a myriad ofdifferent types of circuit devices used in electronics, such as, forexample, microprocessors, graphics processors, application specificintegrated circuits, memory devices or the like, and may be single ormulti-core. If the semiconductor die 195 is implemented as a multi-coredevice, then each of the semiconductor devices may be positioned overand electrically tied to a particular core. For example, the devices 200and 210 are positioned near and electrically coupled to respective coresthat are represented schematically by the dashed boxes 217 and 219.Optionally, groups of such devices 200, 210 etc. may be tied to a givencore.

In the foregoing illustrative embodiments, conductor bumps or balls areused to establish electrical connectivity between one semiconductordevice mounted on another. However, other types of conductor structuresmay be used. FIG. 10 depicts an alternate exemplary embodiment in whicha semiconductor die 220 is provided with the same conductor structures80, 110 and 130, metallization layer 120 and encapsulation layer 40.External conductivity may be provided by the aforementioned conductorstructures 45. However, electrical connections between a mountedsemiconductor die 230 and the semiconductor die 220 may be establishedby way of conductor posts or pillars 240 that are positioned betweencorresponding conductor structures 90 of the semiconductor die 230 andcorresponding conductor structures 80 of the semiconductor die 220. Theconductor posts 250 may be composed of, for example, copper, nickel,gold, platinum, silver, alloys of these or the like. Various fabricationtechniques may be used, such as plating, chemical vapor deposition,physical vapor deposition or the like.

It should be understood that the fabrication processes described hereinmay be performed on an individual single die or currently on multipledie that are part of some larger semiconductor workpiece, such as awafer. The wafer can then be singulated into individual dice.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. An apparatus, comprising: a first semiconductor die having a firstbulk semiconductor side and a first opposite side, the first oppositeside including a metal layer; a second semiconductor die having a secondbulk semiconductor side and a second opposite side, the second oppositeside of the second semiconductor die being coupled to the first oppositeside of the first semiconductor die, the second semiconductor dieincluding electrical connections with the first semiconductor die; aplurality of conductor structures on the metal layer, each of theconductor structures including a conductor post and a solder structurecoupled to the conductor post and extending away from the first oppositeside of the first semiconductor die farther than the second bulksemiconductor side of the second semiconductor die; and wherein thesecond semiconductor die and a least portion of each of the conductorstructures is encapsulated.
 2. The apparatus of claim 1, wherein theelectrical connections comprise solder structures or conductor pillars.3. The apparatus of claim 1, comprising a first substrate coupled to thefirst or second semiconductor die.
 4. The apparatus of claim 1, whereinthe first semiconductor die comprises a processor.
 5. The apparatus ofclaim 4, wherein the semiconductor die comprises a memory device.
 6. Theapparatus of claim 1, wherein the first semiconductor die comprises aplurality of cores.
 7. An apparatus, comprising: a first semiconductordie having a first bulk semiconductor side and a first opposite side,the first opposite side including a metal layer; a plurality of secondsemiconductor dice, each of the second semiconductor dice includingelectrical connections with the first semiconductor die and having asecond bulk semiconductor side and a second opposite side, the secondopposite side being coupled to the first opposite side of the firstsemiconductor die. a plurality of conductor structures on the metallayer, each of the conductor structures including a conductor post and asolder structure coupled to the conductor post and extending away fromthe first opposite side of the first semiconductor die farther than thesecond bulk semiconductor sides of the second semiconductor dice; andwherein the second semiconductor dice and a least portion of each of theconductor structures is encapsulated.
 8. The apparatus of claim 7,wherein the first semiconductor die comprises a processor.
 9. Theapparatus of claim 8, wherein each of the plurality of secondsemiconductor dice comprises a memory device.
 10. The apparatus of claim7, comprising a first substrate coupled to the first or secondsemiconductor die.
 11. The apparatus of claim 10, comprising a secondsubstrate coupled to the first substrate.
 12. The apparatus of claim 7,wherein the first semiconductor die comprises a plurality of cores. 13.An apparatus, comprising: a first semiconductor die having a first bulksemiconductor side and a first opposite side, the first opposite sideincluding a metal layer; a second semiconductor die having a second bulksemiconductor side and a second opposite side, the second opposite sideof the second semiconductor die being coupled to the first opposite sideof the first semiconductor die, the second semiconductor die includingelectrical connections with the first semiconductor die; a plurality ofconductor structures on the metal layer, each of the conductorstructures including a conductor post and a solder structure coupled tothe conductor post and extending away from the first opposite side ofthe first semiconductor die farther than the second bulk semiconductorside of the second semiconductor die; wherein the second semiconductordie and a least portion of each of the conductor structures isencapsulated; and a circuit board coupled to the first semiconductordie.
 14. The apparatus of claim 13, wherein the circuit board comprisesa package substrate.
 15. The apparatus of claim 14, comprising a firstsubstrate coupled to the circuit board to an electronic device.
 16. Theapparatus of claim 13, wherein the electrical connections comprisesolder structures or conductor pillars.
 17. The apparatus of claim 13,wherein the first semiconductor die comprises a processor.
 18. Theapparatus of claim 17, wherein the semiconductor die comprises a memorydevice.
 19. The apparatus of claim 13, wherein the first semiconductordie comprises a plurality of cores.